The present invention relates to an interpolation circuit for producing and outputting correct data in place of an error sample data, which exists in an encoded digital signal obtained by sampling and quantizing an analog information sequentially, as a concealed data by the concealing operation of other correct sample data and, more particularly, to an interpolation circuit suitable for digital processing of video signals as in a digital VTR.
In a case where analog information signals are audio signals, the known error concealing circuit for the encoded data of the prior art is exemplified by a prevalue holding circuit for holding the sample data immediately before the error data and substituting it for the error data or an averaging interpolation circuit for averaging the sample data before and after the error data and using the averaged data as the concealed data in place of the error data, as disclosed in "Digital/Audio" (edited by Doi and Iga and published by Radio Gijutsusha), pp. 209 and 210.
In the interpolation circuit using the pre-value holding circuit or averaging interpolation circuit to be applied to the digital audio signals, no consideration is given to the interpolation accuracy when the correlation between the adjacent sample data is loose, as in the case of a composite video signal where a color signal component is superposed on a luminance signal component. If the interpolation circuit is applied to video signals having a small correlation between the adjacent sample data, the concealing error is enlarged to raise a problem that the image quality is seriously deteriorated in the case where the video signals are displayed in the monitor.
In the case where the analog information signals are the video signals, on the other hand, there is known an error correction (dropout compensation) circuit for substituting the error data with the data, which is extracted from the signal in a horizontal scanning period preceding the horizontal scanning period containing the error data by one, as disclosed in Japanese Patent Laid-Open No. 56-149190. If this error correction circuit is applied to composite video signals, the signals (or data) preceding the horizontal scanning line (or signal line), in which the error data is generated, by one and is stored in a memory. The signals are then read out and separated into luminance signal components and color signal components and are then delayed by respectively suitable time periods of one line. The color signal components are adjusted to the phase corresponding to the color burst phase of the signal line, on which the error data is generated, and are then composed so that they are substituted for the signal line containing the error data.
According to this technique, however, the delay value is added or subtracted for adjusting the color signal components in phase so that no consideration is given to the highly accurate interpolation to raise the problem of the deterioration in the image quality inevitably. Moreover, a circuit for separating the composite video signal into the luminance signal components and the color signal components is also required to raise another problem of enlarging the circuit scale.